This invention relates to a pneumatic tire and to a pneumatic tire mounted on a rim, and more particularly to an elliptically-shaped pneumatic passenger tire and to such a tire mounted on a rim.
It is well understood in the tire and automobile industries that a tire must exhibit certain performance characteristics and meet certain minimum performance standards before it is commercially acceptable. Among such characteristics and standards are those directed to rolling resistance, ride harshness and vibration, ride handling, traction, tread wear, durability, noise and the like.
It is further understood that the design of a tire entails the use of various materials as tire components and their placement within the tire in order to provide a combination which achieves commercially acceptable performance characteristics and standards. Because of the complex nature of the interaction of the materials and components of a tire, it is generally accepted that certain trade-offs are necessary in meeting the foregoing performance characteristics and standards. Additionally, the degree and extent of such trade-offs are not known until the tire is actually made and its performance and characteristics evaluated.
One of the more well-known trade-off's taken into account in tire design and construction is that rolling resistance can be decreased by increasing tire inflation pressure. A further trade-off which is taken into account is that as the tire inflation pressure is increased, the ride harshness and vibration also increases. Therefore, in tire design and construction, taking these and other factors involved into consideration, some degree of rolling resistance is generally sacrificed by using lower inflation pressures in order to achieve acceptable smoothness and comfort in riding or ride harshness and vibration.
Rolling resistance may be expressed by using several different test results. Such tests can be directed to the distance a vehicle travels at constant speed on a specified quantity of fuel, the distance to rest a vehicle travels after it is at constant speed and its power train disengaged from the wheels, or by the amount of drag exerted by the tire when running at a constant speed. The most widely-known form of expressing rolling resistance is in terms of drag. In one test to determine drag the torque of a tire being rotated at a constant speed by frictional engagement with a driving flywheel is determined and then translated into drag.
Ride harshness and vibration is determined by a subjective test in which a vehicle, with the tires to be tested, is driven over a prescribed course and rated by the driver with respect to various ride attributes which are felt or perceived by the driver in the vehicle under typical driving conditions generally experienced by the average motorist. For relatively smooth roads or course, vibration is evaluated, and for relatively rough roads or course, ride harshness is determined.
From the foregoing it can be appreciated that a pneumatic tire which exhibits a decrease in rolling resistance over conventional pneumatic tires and still meets or exhibits commercially accepted performance standards and characteristics would represent an advancement in this art. Further, it would afford a significant contribution to the automobile industry and the millions of motoring public since a decrease in rolling resistance increases fuel economy in the ratio of approximately 5 to 1, based on industry data by plotting fuel economy against rolling resistance. Thus, for example, a 20% decrease in rolling resistance is considered to be approximately equivalent to an increase of 4% in fuel economy. Stated somewhat differently, a passenger vehicle using conventional tires and obtaining 24 miles per gallon could save as much as one mile per gallon in fuel consumption, or approximately 20 additional miles for a tankful of fuel.
As will be more fully discussed hereinafter, and improved elliptically-shaped pneumatic tire under inflation pressures of up to 50% or more than inflation pressures used in conventional tires exhibits a significant decrease in rolling resistance while meeting or exceeding other tire performance characteristics and standards, including ride harshness and vibrations, and thus represents an advancement in this art as well as a significant contribution to the industry.